托福阅读真题Official 45 Passage 2（五）

托福阅读真题Official 45 Passage 2（五）

The Beringia Landscape

During the peak of the last ice age,northeast Asia(Siberia)and Alaska were connected by a broad land mass called the Bering Land Bridge.This land bridge existed because so much of Earth’s water was frozen in the great ice sheets that sea levels were over 100 meters lower than they are today.Between 25,000 and 10,000 years ago,Siberia,the Bering Land Bridge,and Alaska shared many environmental characteristics.These included a common mammalian fauna of large mammals,a common flora composed of broad grasslands as well as wind-swept dunes and tundra,and a common climate with cold,dry winters and somewhat warmer summers.The recognition that many aspects of the modern flora and fauna were present on both sides of the Bering Sea as remnants of the ice-age landscape led to this region being named Beringia.

It is through Beringia that small groups of large mammal hunters,slowly expanding their hunting territories,eventually colonized North and South America.On this archaeologists generally agree,but that is where the agreement stops.One broad area of disagreement in explaining the peopling of the Americas is the domain of paleoecologists,but it is critical to understanding human history:what was Beringia like?

The Beringian landscape was very different from what it is today.Broad,windswept valleys;glaciated mountains;sparse vegetation;and less moisture created a rather forbidding land mass.This land mass supported herds of now-extinct species of mammoth,bison,and horse and somewhat modern versions of caribou,musk ox,elk,and saiga antelope.These grazers supported in turn a number of impressive carnivores,including the giant short-faced bear,the saber-tooth cat,and a large species of lion.

The presence of mammal species that require grassland vegetation has led Arctic biologist Dale Guthrie to argue that while cold and dry,there must have been broad areas of dense vegetation to support herds of mammoth,horse,and bison.Further,nearly all of the ice-age fauna had teeth that indicate an adaptation to grasses and sedges;they could not have been supported by a modern flora of mosses and lichens.Guthrie has also demonstrated that the landscape must have been subject to intense and continuous winds,especially in winter.He makes this argument based on the anatomy of horse and bison,which do not have the ability to search for food through deep snow cover.They need landscapes with strong winds that remove the winter snows,exposing the dry grasses beneath.Guthrie applied the term“mammoth steppe”to characterize this landscape.

In contrast,Paul Colinvaux has offered a counterargument based on the analysis of pollen in lake sediments dating to the last ice age.He found that the amount of pollen recovered in these sediments is so low that the Beringian landscape during the peak of the last glaciation was more likely to have been what he termed a“polar desert,”with little or only sparse vegetation.In no way was it possible that this region could have supported large herds of mammals and thus,human hunters.Guthrie has argued against this view by pointing out that radiocarbon analysis of mammoth,horse,and bison bones from Beringian deposits revealed that the bones date to the period of most intense glaciation.

The argument seemed to be at a standstill until a number of recent studies resulted in a spectacular suite of new finds.The first was the discovery of a 1,000-square-kilometer preserved patch of Beringian vegetation dating to just over 17,000 years ago—the peak of the last ice age.The plants were preserved under a thick ash fall from a volcanic eruption.Investigations of the plants found grasses,sedges,mosses,and many other varieties in a nearly continuous cover,as was predicted by Guthrie.But this vegetation had a thin root mat with no soil formation,demonstrating that there was little long-term stability in plant cover,a finding supporting some of the arguments of Colinvaux.A mixture of continuous but thin vegetation supporting herds of large mammals is one that seems plausible and realistic with the available data.

Question 9 of 14

According to paragraph 4,which of the following is NOT an adaptation that helps ensure that pollen travels as far as possible?

A.Pollen-producing flowers and catkins are located at or near the top of the tree.

B.Trees grow at least 100 meters away from each other.

C.Dangling catkins release pollen only when the wind is blowing hard.

D.Pollen is not released during rain storms or when the air is damp.

正确答案：B

题目详解

题型分类：否定事实信息题

原文定位：根据选项定位

选项分析：

B选项与第五句only between 0.5 percent and 40 percent gets more than 100 meters away from the parent矛盾。既然很少有树可以离开母树100米远，那么传粉肯定对距离近的树更有利。

A选项the top of the tree对应第一句the top branches。

C选项when the wind is blowing hard对应第二句the wind is strong enough to bend them。

D选项对应第四句when the air is dry。

Question 10 of 14

The word“significant”in the passage is closest in meaning to

A.sufficient

B.considerable

C.increasing

D.small

正确答案：B

题目详解

题型分类：词汇题

选项分析：

原句“但是当这么远的时候，significant数量可以离开一千米或更远”。前一句说很少有花粉能离开一百米，而这一句开头的but表明这一句和上一句是转折关系；可以推测significant表示数量多。B选项considerable意思为“相当大的”，符合题意。Significant原意为“大量的”。

A选项sufficient充分的。

C选项increasing不断增加的。

D选项small小的。